Hydrocarbon compounds are useful for a number of purposes. In particular, hydrocarbon compounds are useful, inter alia, as fuels, solvents, degreasers, cleaning agents, and polymer precursors. The most important source of hydrocarbon compounds is petroleum crude oil. Refining of crude oil into separate hydrocarbon compound fractions is a well-known processing technique.
Crude oils range widely in their composition and physical and chemical properties. In the last two decades, the need to process heavier crude oils has increased. Heavy crudes are characterized by a relatively high viscosity and low API gravity (generally lower than 25°) and high percentage of high boiling components (>950° F.).
Refined petroleum products generally have higher average hydrogen to carbon ratios on a molecular basis. Therefore, the upgrading of a petroleum refinery hydrocarbon fraction is classified into one of two categories: hydrogen addition and carbon rejection. Hydrogen addition is performed by processes such as hydrotreating and hydrocracking. Carbon rejection processes typically produce a stream of rejected high carbon material which may be a liquid or a solid; e.g., coke deposits.
Some carbon rejection processes such as FCC and coking include cracking of heavy molecules. Others such as solvent deasphalting consist only of physical separation of the lighter and heavier hydrocarbons. For instance, in solvent deasphalting of a heavy oil, a light solvent such as a C3/C4/C5 hydrocarbon is used to dissolve or suspend the lighter hydrocarbons allowing the asphaltenes to be “precipitated”. These phases are separated and then the solvent is recovered. Additional information on solvent deasphalting conditions, solvents and operations may be obtained from U.S. Pat. Nos. 4,239,616; 4,440,633; 4,354,922; and, 4,354,928, all of which are incorporated herein by reference.
To facilitate processing, heavy crudes or their fractions are generally subjected to thermal cracking or hydrocracking to convert the higher boiling fractions to lower boiling fractions, followed by hydrotreating to remove heteroatoms such as sulfur, nitrogen, oxygen and metallic impurities.
Further information on hydrotreating catalysts, techniques and operating conditions for residue feeds may be obtained by reference to U.S. Pat. Nos. 5,198,100; 4,810,361; 4,810,363; 4,588,709; 4,776,945 and 5,225,383 which are incorporated herein for this teaching.
Crude petroleums with greater amounts of impurities including asphaltenes, metals, organic sulfur and organic nitrogen require more severe processing to remove them. Generally speaking, the more severe the conditions required to treat a given feedstock (e.g. higher temperature and pressures), the greater the cost of overall plant.
In particular, asphaltenes produce high amounts of coke which deactivates the hydrotreating and hydrocracking catalysts. Asphaltenes also form precipitates and contain precipitate precursors which can greatly hinder subsequent processing.
Worldwide, fixed-bed reactors are still utilized considerably more than ebullated-bed reactors. The fixed-bed system is used for lighter, cleaner feedstocks and is a relatively simple and well understood system. Fixed-bed systems are used mostly for naphtha, mid-distillate, atmospheric and vacuum gas-oils, and atmospheric residua treatment.
However, as the feedstock becomes heavier, has a greater level of impurities, or requires more severe conversion levels, the fixed-bed system becomes less effective and efficient. In these cases, the ebullated-bed reactor systems are better suited for processing.
In general, ebullated-bed reactors are utilized to process heavy crude oil feed streams, particularly those feeds with high metals and CCR. The ebullated-bed process comprises the passing of concurrently flowing streams of liquids, or slurries of liquids and solids, and gas through a vertically elongated fluidized catalyst bed. The catalyst is fluidized and completely mixed by the upwardly flowing liquid streams. The ebullated-bed process has commercial application in the conversion and upgrading of heavy liquid hydrocarbons and converting coal to synthetic oils.
The ebullated-bed reactor and related process is generally described in U.S. Pat. No. 25,770 to Johanson incorporated herein by reference. A mixture of hydrocarbon liquid and hydrogen is passed upwardly through a bed of catalyst particles at a rate such that the particles are forced into random motion as the liquid and gas pass upwardly through the bed. The catalyst bed motion is controlled by a recycle liquid flow so that at steady state, the bulk of the catalyst does not rise above a definable level in the reactor. Vapors, along with the liquid which is being hydrogenated, pass through the upper level of catalyst particles into a substantially catalyst free zone and are removed from the upper portion of the reactor.
Ebullated-bed reactors are generally operated at relatively high temperatures and pressures in order to process these heavy feedstocks. Since such operating parameters substantially increase the cost of designing and constructing the reactors, it would therefore be advantageous to have a system wherein the overall design and manufacturing costs were optimized for specific feedstocks or feedstock components. This optimization would result in a lower initial investment and lower annual operating costs. Moreover, there is always a need to design process systems that convert greater amounts of feedstock into high quality products.